Percussion compactors (also known as rammers and tampers) are well known in the construction industry and are used to compact soil and other loose materials in a variety of construction and excavation operations. Such devices are typically manually operated by a single operator. A percussion rammer is distinguishable from a vibration (or vibratory) compactor in terms of both amplitude and frequency of operation. A percussion rammer may operate with a vertical amplitude of approximately 2-3 inches (50-75 mm) and a frequency of about 600-800 cycles per minute (cpm). A vibratory compactor, on the other hand, may operate with a much smaller vertical amplitude, e.g., 0.060 inch (about 1.5 mm) and a much higher frequency, e.g., 4,000-6,000 cpm.
A typical percussion rammer thus provides a generally vertically oriented, large amplitude movement to a flat soil engaging shoe that compacts the soil with a pounding type of movement. The compacting shoe is typically mounted with its flat surface at an angle slightly less than 90° to the vertical and, as a result, the operating axis along which the percussive tamping movement is transmitted is slightly forwardly-inclined. The angle of operating movement may be, for example, 15° to the vertical. This angled orientation results in a forward component of motion with every stroke and permits the operator to guide the machine in a forward operating path over the surface by grasping a horizontal operator handle at the rear of the machine. The operator handle is typically attached to the rear of a frame that includes two generally horizontal laterally spaced components that are attached by their opposite forward ends to a cushioning pivot mechanism near the upper end of the operating axis. The cushioning pivot arrangement typically comprises a pair of large elastomeric elements interposed between the forward ends of the lateral frame members and the body of the machine, so the frame and operator handle may pivot vertically relative to the rammer as it moves up and down. This arrangement helps isolate the generally vertical component of operating movement from the operator handle and the hands of the operator grasping the handle. However, because of the inclined orientation of the operating axis of the machine, there is a significant horizontal component of movement that the torsional mounting of the side frame to the machine does little to damp or isolate. This horizontal component of movement is thus transmitted directly through the side frame members to the operator handle and the hands of the operator.
Worker safety regulations worldwide have examined the effects of hand/arm vibration levels in manually operated vibratory equipment. Some jurisdictions have effected regulations that apply measured vibration levels to operating time to make sure that operators are given periodic rests while using such equipment. Various solutions have been proposed to reduce vibration levels experienced by the machine operator, with the expectation that such lower levels may increase allowable operator time and/or reduce the length and/or frequency of operator periods.
One such solution is described in U.S. Pat. No. 6,749,365. In this solution, an operator handle assembly is provided for a percussive soil compacting device to isolate generally horizontal components of operating movement from the hands of the operator, the assembly including a main frame attached at one end to the compacting device, and a manually engageable operator handle attached to the other end of the main frame with a shock absorbing mount oriented to absorb generally horizontal components of operating movement. In a preferred embodiment, the main frame includes a pair of laterally spaced frame members having ends adjacent the operator handle and the operator handle includes a generally horizontal manually engageable member having opposite lateral ends; the shock absorbing mount comprises a pair of torsionally resilient shock absorbers each of which is attached with a first connector to an end of said frame member and with a second connector to a lateral end of the operator handle, the first and second connectors oriented to position the shock absorbers on a common torsional axis that is vertically offset from and generally parallel to the horizontal member. The shock absorbers preferably comprise elastomeric elements, each element being mounted between said first and second connectors.
A principal drawback of such solutions is that they still require the operator to maintain contact with the percussive soil compactor for extended periods of time, during which he or she continues to absorb vibrations. Even though such vibrations may be reduced in magnitude, the long-term effects on operators who regularly use such equipment over extended periods is unknown at best—and potentially very hazardous. It would be beneficial, then, to address these known and potential problems by eliminating the need for the operator to maintain contact with a percussive soil compactor during its operation.